Composition for solar cell electrodes and electrode fabricated using the same

ABSTRACT

A composition for solar cell electrodes includes a silver powder; a glass frit; and an organic vehicle, wherein the glass frit includes bismuth (Bi), tellurium (Te), and chromium (Cr).

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application based on application Ser. No.14/534,370, filed Nov. 6, 2014, now U.S. Pat. No. 9,039,937, the entirecontents of which is hereby incorporated by reference.

Korean Patent Application Nos. 10-2013-0157659, filed on Dec. 17, 2013,and 10-2014-0124652, filed on Sep. 18, 2014, in the Korean IntellectualProperty Office, and entitled: “Composition for Solar Cell Electrodesand Electrode Fabricated Using the Same,” are incorporated by referenceherein in their entirety.

BACKGROUND

1. Field

Embodiments relate to a composition for solar cell electrodes andelectrodes fabricated using the same.

2. Description of the Related Art

Solar cells generate electric energy using the photovoltaic effect of ap-n junction which converts photons of sunlight into electricity. In thesolar cell, front and rear electrodes are formed on upper and lowersurfaces of a semiconductor wafer or substrate with the p-n junction,respectively. Then, the photovoltaic effect of the p-n junction isinduced by sunlight entering the semiconductor wafer and electronsgenerated by the photovoltaic effect of the p-n junction provideelectric current to the outside through the electrodes.

SUMMARY

Embodiments are directed to a composition for solar cell electrodesincluding

a silver powder, a glass frit, and an organic vehicle. The glass fritincludes bismuth (Bi), tellurium (Te), and chromium (Cr).

A mole ratio of chromium to tellurium may range from about 1:1 to about1:80.

The glass frit may further include at least one element selected fromlead (Pb), lithium (Li), zinc (Zn), tungsten (W), phosphorus (P),silicon (Si), magnesium (Mg), cesium (Ce), strontium (Sr), molybdenum(Mo), titanium (Ti), tin (Sn), indium (In), vanadium (V), barium (Ba),nickel (Ni), copper (Cu), sodium (Na), potassium (K), antimony (Sb),germanium (Ge), gallium (Ga), calcium (Ca), arsenic (As), cobalt (Co),zirconium (Zr), manganese (Mn), aluminum (Al), and boron (B).

The glass frit may include about 5 mol % to about 50 mol % of lead (Pb)based on a total weight of the glass frit.

The glass frit may be prepared from a mixture of metal oxides includingabout 5 wt % to about 30 wt % of bismuth oxide, about 40 wt % to about80 wt % of tellurium oxide, about 1 wt % to about 15 wt % of chromiumoxide, and about 1 wt % to about 50 wt % of a fourth metal oxide.

The fourth metal oxide may include at least one metal oxide selectedfrom lead (Pb), lithium (Li), zinc (Zn), tungsten (W), phosphorus (P),silicon (Si), magnesium (Mg), cesium (Ce), strontium (Sr), molybdenum(Mo), titanium (Ti), tin (Sn), indium (In), vanadium (V), barium (Ba),nickel (Ni), copper (Cu), sodium (Na), potassium (K), antimony (Sb),germanium (Ge), gallium (Ga), calcium (Ca), arsenic (As), cobalt (Co),zirconium (Zr), manganese (Mn), aluminum (Al), and boron (B) oxides.

The fourth metal oxide may include about 1 wt % to about 10 wt % oflithium oxide, about 1 wt % to about 10 wt % of zinc oxide, and about 1wt % to about 10 wt % of tungsten oxide based on the total weight of themixture of metal oxides.

The fourth metal oxide may include about 15 wt % to about 50 wt % oflead oxide (PbO) based on a total weight of the mixture of metal oxides.

The composition may include about 60 wt % to about 95 wt % of the silverpowder, about 0.5 wt % to about 20 wt % of the glass fit, and about 1 wt% to about 30 wt % of the organic vehicle.

The glass frit may have an average particle diameter (D50) of about 0.1μm to about 10 μm.

The composition may further include at least one additive selected froma dispersant, a thixotropic agent, a plasticizer, a viscositystabilizer, an anti-foaming agent, a pigment, a UV stabilizer, anantioxidant, and a coupling agent.

The organic vehicle may include a binder resin, the binder resin havinga weight average molecular weight (Mw) of about 30,000 g/mol to about200,000 g/mol.

The composition may have a viscosity of about 100,000 cps to about500,000 cps.

Embodiments are also directed to a solar cell electrode fabricated usingthe composition for solar cell electrodes as described above.

BRIEF DESCRIPTION OF THE DRAWING

Features will become apparent to those of skill in the art by describingin detail exemplary embodiments with reference to the attached drawingin which:

The FIGURE illustrates a schematic view of a solar cell in accordancewith one embodiment.

DETAILED DESCRIPTION

Example embodiments will now be described more fully hereinafter withreference to the accompanying drawing; however, they may be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey exemplary implementations to those skilled in the art.

In the drawing figure, the dimensions of layers and regions may beexaggerated for clarity of illustration. It will also be understood thatwhen a layer or element is referred to as being “on” another layer orsubstrate, it can be directly on the other layer or substrate, orintervening layers may also be present.

Composition for Solar Cell Electrodes

A composition for solar cell electrodes according to embodiments mayinclude a silver powder, a glass frit including bismuth (Bi), tellurium(Te), and chromium (Cr), for example, elemental bismuth (Bi), tellurium(Te), and chromium (Cr), and an organic vehicle.

(A) Silver Powder

The composition for solar cell electrodes according to embodiments mayinclude a silver (Ag) powder as a conductive powder. The particle sizeof the silver powder may be nanometer or micrometer scale. For example,the silver powder may have a particle size of dozens to several hundrednanometers, or several to dozens of micrometers. In otherimplementations, the silver powder may be a mixture of two or more typesof silver powders having different particle sizes.

The silver powder may have a spherical, flake or amorphous shape. In oneimplementation, the silver powder may have an average particle diameter(D50) of about 0.1 μm to about 10 μm, for example about 0.5 μm to about5 μm. The average particle diameter may be measured using, for example,a Model 1064D (CILAS Co., Ltd.) after dispersing the conductive powderin isopropyl alcohol (IPA) at 25° C. for 3 minutes via ultrasonication.Within this range of average particle diameter, the composition mayprovide low contact resistance and low line resistance.

The silver powder may be present in an amount of about 60 wt % to about95 wt % based on the total weight of the composition. Within this range,the conductive powder may prevent deterioration in conversion efficiencydue to an increase in resistance. For example, the conductive powder maybe present in an amount of about 70 wt % to about 90 wt %. In someembodiments, the silver powder may be present in an amount of about 60wt %, 61 wt %, 62 wt %, 63 wt %, 64 wt %, 65 wt %, 66 wt %, 67 wt %, 68wt %, 69 wt %, 70 wt %, 71 wt %, 72 wt %, 73 wt %, 74 wt %, 75 wt %, 76wt %, 77 wt %, 78 wt %, 79 wt %, 80 wt %, 81 wt %, 82 wt %, 83 wt %, 84wt %, 85 wt %, 86 wt %, 87 wt %, 88 wt %, 89 wt %, 90 wt %, 91 wt %, 92wt %, 93 wt %, 94 wt %, or 95 wt % based on the total weight of thecomposition.

(B) Glass Frit Including Bismuth (Bi), Tellurium (Te), and Chromium (Cr)

The glass frit may serve to enhance adhesion between the conductivepowder and the wafer or the substrate and to form silver crystal grainsin an emitter region by etching an anti-reflection layer and melting thesilver powder so as to reduce contact resistance during a baking processof the electrode paste. Further, during the sintering process, the glassfrit may be softened and may decrease the baking temperature.

When the area of the solar cell is increased in order to improve solarcell efficiency, there is a possibility that contact resistance of thesolar cell may be increased. Thus, it is desirable to minimize theinfluence on the p-n junction while minimizing serial resistance (Rs)and maximizing open circuit voltage (Voc). In addition, the bakingtemperature may vary within a broad range with increasing use of variouswafers having different sheet resistances. It is desirable that theglass frit secure sufficient thermal stability to withstand a wide rangeof baking temperatures.

Solar cells may be connected to each other by a ribbon to constitute asolar cell battery. In this case, there is a possibility that lowadhesive strength between solar cell electrodes and the ribbon may causedetachment of the cells or deterioration in reliability.

According to embodiments, in order to ensure that the solar cell hasdesirable electrical and physical properties such as conversionefficiency and adhesive strength, a glass frit including bismuth (Bi),tellurium (Te), and chromium (Cr) is used.

In an implementation, a mole ratio of chromium (Cr) to tellurium (Te)may range from about 1:1 to about 1:80. Within this range, solar cellelectrodes fabricated using the glass frit may exhibit excellentadhesive strength with respect to a ribbon and excellent conversionefficiency, while securing low serial resistance and contact resistance.In some embodiments, a mole ratio of chromium to tellurium may rangefrom about 1:1 to about 1:40, for example, about 1:5 to about 1:35.

In some embodiments, in addition to bismuth (Bi), tellurium (Te), andchromium (Cr), the glass frit may further include at least one elementselected from lead (Pb), lithium (Li), zinc (Zn), tungsten (W),phosphorus (P), silicon (Si), magnesium (Mg), cesium (Ce), strontium(Sr), molybdenum (Mo), titanium (Ti), tin (Sn), indium (In), vanadium(V), barium (Ba), nickel (Ni), copper (Cu), sodium (Na), potassium (K),antimony (Sb), germanium (Ge), gallium (Ga), calcium (Ca), arsenic (As),cobalt (Co), zirconium (Zr), manganese (Mn), aluminum (Al), and boron(B).

In particular, in addition to bismuth (Bi), tellurium (Te), and chromium(Cr), the glass frit may further include about 5 mol % to about 50 mol %of lead (Pb), for example, elemental lead (Pb), based on the totalweight of the glass frit. The glass frit may provide excellent effectsin terms of processability (process window). In some embodiments, lead(Pb) may be present in an amount of about 5 mol %, 6 mol %, 7 mol %, 8mol %, 9 mol %, 10 mol %, 11 mol %, 12 mol %, 13 mol %, 14 mol %, 15 mol%, 16 mol %, 17 mol %, 18 mol %, 19 mol %, 20 mol %, 21 mol %, 22 mol %,23 mol %, 24 mol %, 25 mol %, 26 mol %, 27 mol %, 28 mol %, 29 mol %, 30mol %, 31 mol %, 32 mol %, 33 mol %, 34 mol %, 35 mol %, 36 mol %, 37mol %, 38 mol %, 39 mol %, 40 mol %, 41 mol %, 42 mol %, 43 mol %, 44mol %, 45 mol %, 46 mol %, 47 mol %, 48 mol %, 49 mol %, or 50 mol %based on the total weight of the glass frit.

The glass fit may be prepared from a mixture of metal oxides includingbismuth oxide, tellurium oxide, chromium oxide, and a fourth metaloxide.

In some embodiments, the fourth metal oxide may include at least onemetal oxide selected from lead (Pb), lithium (Li), zinc (Zn), tungsten(W), phosphorus (P), silicon (Si), magnesium (Mg), cesium (Ce),strontium (Sr), molybdenum (Mo), titanium (Ti), tin (Sn), indium (In),vanadium (V), barium (Ba), nickel (Ni), copper (Cu), sodium (Na),potassium (K), antimony (Sb), germanium (Ge), gallium (Ga), calcium(Ca), arsenic (As), cobalt (Co), zirconium (Zr), manganese (Mn),aluminum (Al), and boron (B) oxides.

In one embodiment, the mixture of metal oxides may include about 5 wt %to about 30 wt % of bismuth oxide; about 40 wt % to about 80 wt % oftellurium oxide; about 1 wt % to about 15 wt % of chromium oxide; andabout 1 wt % to about 50 wt % of the fourth metal oxide. Within thisrange, the glass frit may secure both excellent adhesive strength andexcellent conversion efficiency.

In some embodiments, the fourth metal oxide may include about 15 wt % toabout 50 wt % of lead oxide (PbO) based on the total weight of themixture of metal oxides. Within this range, the glass frit may provideexcellent effects in terms of processability (process window). In someembodiments, lead oxide may be present in an amount of about 15 wt %, 16wt %, 17 wt %, 18 wt %, 19 wt %, 20 wt %, 21 wt %, 22 wt %, 23 wt %, 24wt %, 25 wt %, 26 wt %, 27 wt %, 28 wt %, 29 wt %, 30 wt %, 31 wt %, 32wt %, 33 wt %, 34 wt %, 35 wt %, 36 wt %, 37 wt %, 38 wt %, 39 wt %, 40wt %, 41 wt %, 42 wt %, 43 wt %, 44 wt %, 45 wt %, 46 wt %, 47 wt %, 48wt %, 49 wt %, or 50 wt %.

In some embodiments, the fourth metal oxide may include lithium oxide(Li₂O), zinc oxide (ZnO), and tungsten oxide (WO₃). For example, thefourth metal oxide may include 1 wt % to 10 wt % of lithium oxide, 1 wt% to 10 wt % of zinc oxide, and 1 wt % to 10 wt % of tungsten oxidebased on the total weight of the mixture of metal oxides. Within thisrange, the glass frit can secure both excellent adhesive strength andexcellent conversion efficiency.

In some embodiments, wherein the glass frit may be prepared from amixture of metal oxides including 5 wt % to 30 wt % of bismuth oxide; 40wt % to 80 wt % of tellurium oxide; 1 wt % to 15 wt % of chromium oxide;and 1 wt % to 10 wt % of lithium oxide, 1 wt % to 10 wt % of zinc oxide,and 1 wt % to 10 wt % of tungsten oxide. Within this range, the glassfrit can secure both excellent adhesive strength and excellentconversion efficiency.

The glass fit may be prepared from such metal oxides by any suitablemethod. For example, the metal oxides may be mixed in a predeterminedratio. Mixing may be carried out using a ball mill or a planetary mill.The mixed composition may be melted at about 900° C. to about 1300° C.,followed by quenching to about 25° C. The obtained resultant may besubjected to pulverization using a disc mill, a planetary mill, or thelike, thereby providing a glass frit.

In some embodiments, the glass frit may have an average particlediameter D50of about 0.1 μm to about 10 μm. The glass frit may have aspherical or amorphous shape.

In some embodiments, the glass frit may be present in an amount of about0.5 wt % to about 20 wt % based on the total amount of the composition.Within this range, the glass frit may secure excellent adhesive strengthand excellent conversion efficiency given varying surface resistanceswhile minimizing serial resistance so as to improve solar cellefficiency. In some embodiments, the glass frit may be present in anamount of about 0.5 wt %, 1 wt %, 1.5 wt %, 2 wt %, 2.5 wt %, 3 wt %,3.5 wt %, 4 wt %, 5 wt %, 6 wt %, 7 wt %, 8 wt %, 9 wt %, 10 wt %, 11 wt%, 12 wt %, 13 wt %, 14 wt %, 15 wt %, 16 wt %, 17 wt %, 18 wt %, 19 wt%, or 20 wt %.

(C) Organic Vehicle

The organic vehicle may impart suitable viscosity and rheologicalcharacteristics for printing to the paste composition through mechanicalmixing with the inorganic component of the composition for solar cellelectrodes.

The organic vehicle may be any suitable organic vehicle used for thecomposition for solar cell electrodes. For example, the organic vehiclemay include a binder resin, a solvent, or the like.

The binder resin may be selected from acrylate resins or celluloseresins. Ethyl cellulose may be used as the binder resin. In otherimplementations, the binder resin may be selected from among ethylhydroxyethylcellulose, nitrocellulose, a mixture of ethylcellulose andphenol resins, alkyd, phenol, acrylate ester, xylene, polybutene,polyester, urea, melamine, vinyl acetate resins, wood rosin,polymethacrylates of alcohols, or the like.

In some embodiments, the binder resin may have a weight averagemolecular weight (Mw) of about 30,000 g/mol to about 200,000 g/mol.Within this range, the binder resin may provide excellent effects interms of printability. By way of example, the binder resin may have aweight average molecular weight of about 40,000 g/mol to about 150,000g/mol.

The solvent may be selected from the group of, for example, hexane,toluene, ethyl cellosolve, cyclohexanone, butyl cellosolve, butylcarbitol(diethylene glycol monobutyl ether), dibutyl carbitol(diethyleneglycol dibutyl ether), butyl carbitol acetate(diethylene glycolmonobutyl ether acetate), propylene glycol monomethyl ether, hexyleneglycol, terpineol, methylethylketone, benzylalcohol, γ-butyrolactone,ethyl lactate, and combinations thereof.

The organic vehicle may be present in an amount of about 1 wt % to about30 wt % based on the total weight of the composition. Within this range,the organic vehicle may provide sufficient adhesive strength andexcellent printability to the composition. In some embodiments, theorganic vehicle may be present in an amount of about 1 wt %, 2 wt %, 3wt %, 4 wt %, 5 wt %, 6 wt %, 7 wt %, 8 wt %, 9 wt %, 10 wt %, 11 wt %,12 wt %, 13 wt %, 14 wt %, 15 wt %, 16 wt %, 17 wt %, 18 wt %, 19 wt %,20 wt %, 21 wt %, 22 wt %, 23 wt %, 24 wt %, 25 wt %, 26 wt %, 27 wt %,28 wt %, 29 wt %, or 30 wt % based on the total weight of thecomposition.

(D) Additives

The composition may further include typical additives, as needed, toenhance flow properties, process properties, and stability. Theadditives may include dispersants, thixotropic agents, plasticizers,viscosity stabilizers, anti-foaming agents, pigments, UV stabilizers,antioxidants, coupling agents, or the like. These additives may be usedalone or as mixtures thereof.

These additives may be present in an amount of about 0.1 wt % to about 5wt % in the composition. This amount may be changed as desired. In someembodiments, the additives may be present in an amount of about 0.1 wt%, 0.2 wt %, 0.3 wt %, 0.4 wt %, 0.5 wt %, 0.6 wt %, 0.7 wt %, 0.8 wt %,0.9 wt %, 1 wt %, 1.5 wt %, 2 wt %, 2.5 wt %, 3 wt %, 3.5 wt %, 4 wt %,4.5 wt %, or 5 wt %.

In addition, the composition for solar cell electrodes may have aviscosity of about 100,000 cps to about 500,000 cps (about 100 kcps toabout 500 kcps). Within this range, the composition may provideexcellent effects in terms of printability. By way of example, thecomposition may have a viscosity of about 250,000 cps to about 400,000cps (about 250 kcps to about 400 kcps).

Solar Cell Electrode and Solar Cell Including the Same

Embodiments are also directed to an electrode formed of the compositionfor solar cell electrodes and a solar cell including the same. FIG. 1illustrates a solar cell in accordance with one embodiment.

Referring to FIG. 1, a rear electrode 210 and a front electrode 230 maybe formed by printing and baking the composition on a wafer or substrate100 that includes a p-layer (or n-layer) 101 and an n-layer (or p-layer)102, which will serve as an emitter. For example, a preliminary processfor preparing the rear electrode 210 is performed by printing thecomposition on the rear surface of the wafer 100 and drying the printedcomposition at about 200° C. to about 400° C. for about 10 seconds toabout 60 seconds. Further, a preliminary process for preparing the frontelectrode may be performed by printing the paste on the front surface ofthe wafer and drying the printed composition. Then, the front electrode230 and the rear electrode 210 may be formed by baking the wafer atabout 400° C. to about 950° C., for example at about 850° C. to about950° C., for about 30 seconds to about 50 seconds.

The following Examples and Comparative Examples are provided in order tohighlight characteristics of one or more embodiments, but it will beunderstood that the Examples and Comparative Examples are not to beconstrued as limiting the scope of the embodiments, nor are theComparative Examples to be construed as being outside the scope of theembodiments. Further, it will be understood that the embodiments are notlimited to the particular details described in the Examples andComparative Examples.

EXAMPLES Example 1

Bismuth oxide, tellurium oxide, and chromium oxide were mixed togetherwith lithium oxide, zinc oxide and tungsten oxide as the fourth metaloxide according to the composition listed in Table 1 and subjected tomelting and sintering at 900° C. to 1,400° C., thereby preparing a glassfrit having an average particle diameter (D50) of 2.0 μm.

As an organic binder, 0.8 wt % of ethylcellulose (STD4, Dow ChemicalCompany)(Mw=50,000 g/mol) was sufficiently dissolved in 8.5 wt % ofbutyl carbitol at 60° C. 86.5 wt % of a spherical silver powder (AG-4-8,Dowa Hightech Co. Ltd.) having an average particle diameter of 2.0 μm,3.5 wt % of the prepared glass frit, 0.2 wt % of a dispersant BYK102(BYK-chemie) and 0.5 wt % of a thixotropic agent Thixatrol ST (ElementisCo., Ltd.) were added to the binder solution, followed by mixing andkneading in a 3-roll kneader, thereby preparing a composition for asolar cell electrodes.

The viscosity of the prepared composition was measured at roomtemperature using a rotary viscometer HBDV-II+Pro (Brookfield Co.,Ltd.). In measurement of the viscometer, a sample cup was completelyfilled with a sample and spindle #14 was mounted on the viscometer.Then, the viscosity was measured at a shear rate of 10 rpm afterstabilizing the temperature for 5 minutes. The obtained result is shownin Table 2.

The prepared composition was deposited over a front surface of acrystalline mono-wafer by screen-printing in a predetermined pattern,followed by drying in an IR drying furnace to prepare a front electrode.Then, the composition for electrodes containing aluminum was printed ona rear side of the wafer and dried in the same manner. Cells formedaccording to this procedure were subjected to baking at 980° C. for 40seconds in a belt-type baking furnace, and evaluated as to serialresistance Rs (Ω), fill factor FF (%), and conversion efficiency (%)using a solar cell efficiency tester CT-801 (Pasan Co., Ltd.). Then,flux was applied to the front electrode of the cells and bonded to aribbon at 300° C. to 400° C. using a soldering iron (Hakko Co., Ltd.).Then, the resultant was evaluated as to adhesive strength (N/mm) at apeeling angle of 180° and a stretching rate of 50 mm/min using atensioner (Tinius Olsen). The measured conversion efficiency, serialresistance, and adhesive strength (N/mm) are shown in Table 2.

Examples 2 to 20 and Comparative Examples 1 to 3

Compositions for solar cell electrodes were prepared and evaluated as tophysical properties in the same manner as in Example 1 except that theglass frits were prepared in compositions as listed in Table 1. Resultsare shown in Table 2.

TABLE 1 Composition of glass frit (unit: wt %) Bi₂O₃ TeO₂ Cr₂O₃ Li₂ONa₂CO₃ ZnO PbO WO₃ Example 1 9.0 76.0 1.0 6.0 — 7.0 — 1.0 Example 2 11.570.5 4.0 5.0 1.0 8.0 — — Example 3 5.0 66.0 15.0 7.0 — 5.0 — 2.0 Example4 23.7 49.8 12.5 4.0 2.0 5.0 — 3.0 Example 5 16.5 67.5 2.0 4.0 1.0 8.0 —1.0 Example 6 30.0 41.0 15.0 9.0 — 5.0 — — Example 7 11.2 62.3 12.5 1.03.0 9.0 — 1.0 Example 8 23.7 54.8 7.5 8.0 2.0 4.0 — — Example 9 5.0 76.05.0 2.0 2.0 8.0 — 2.0 Example 10 14.0 69.0 3.0 7.0 — 7.0 — — Example 1130.0 51.0 5.0 2.0 1.0 7.0 — 4.0 Example 12 11.2 67.3 7.5 4.0 2.0 5.0 —3.0 Example 13 9.0 72.0 5.0 9.0 — 3.0 — 2.0 Example 14 19.0 62.0 5.0 8.02.0 4.0 — — Example 15 19.0 66.0 1.0 7.0 1.0 5.0 — 1.0 Example 16 11.572.5 2.0 6.0 1.0 6.0 — 1.0 Example 17 17.5 58.5 10.0 7.0 2.0 4.0 — 1.0Example 18 16.5 65.5 4.0 6.0 — 7.0 — 1.0 Example 19 9.0 66.5 1.0 1.0 —7.0 14.5 1.0 Example 20 5.0 41.0 1.0 0.8 — 2.0 50.2 — Comparative 8.070.0 — 6.0 1.0 8.0 — 7.0 Example 1 Comparative 10.0 86.0 — 3.0 — 1.0 — —Example 2 Comparative 11.0 73.5 — 5.0 1.0 7.0 — 2.5 Example 3

TABLE 2 Vis- Serial Effi- Adhesive Mole cosity Resistance Fill ciencyStrength ratio (kcps) (mΩ) Factor (%) (N/mm) (Te/Cr) Example 1 312 2.6477.22 16.77 5.7 36.188 Example 2 351 2.69 77.04 16.72 5.0 8.392 Example3 321 2.92 76.83 16.65 6.0 2.095 Example 4 333 2.95 76.75 16.63 4.61.895 Example 5 315 2.70 76.99 16.70 4.0 16.070 Example 6 324 2.89 76.8916.67 4.7 1.302 Example 7 322 2.93 76.76 16.63 4.6 2.371 Example 8 3462.85 76.90 16.67 4.7 3.476 Example 9 327 2.70 76.99 16.70 5.6 7.238Example 328 2.31 77.31 16.80 4.9 10.952 10 Example 330 2.76 76.96 16.695.6 4.857 11 Example 325 2.76 76.96 16.69 4.0 4.270 12 Example 319 2.6777.10 16.74 4.9 6.857 13 Example 315 2.71 76.99 16.70 4.9 5.904 14Example 327 2.55 77.28 16.79 5.5 31.427 15 Example 334 2.67 77.05 16.724.8 17.261 16 Example 341 2.81 76.94 16.68 4.5 2.786 17 Example 325 2.7077.00 16.71 5.4 7.797 18 Example 334 2.95 77.00 16.71 5.2 31.665 19Example 328 2.64 76.90 16.67 4.9 19.523 20 Compar- 324 3.00 71.54 15.053.3 — ative Example 1 Compar- 350 3.22 72.06 15.28 3.3 — ative Example 2Compar- 336 3.03 71.45 14.93 2.7 — ative Example 3

It can be seen in Table 2, that the solar cell electrodes fabricatedusing the compositions prepared in Examples 1 to 20 exhibitedconsiderably higher adhesive strength with respect to ribbons as well aslower serial resistance and excellent fill factor and conversionefficiency, as compared with those of Comparative Examples 1 to 3wherein the compositions of the glass frits were not within the scope ofembodiments.

By way of summation and review, The electrodes of the solar cell may beformed on a wafer by applying, patterning, and baking a composition forelectrodes.

Continuous reduction in emitter thickness for improvement of solar cellefficiency may cause shunting, which can deteriorate solar cellperformance. In addition, as the area of solar cells has graduallyincreased in area to achieve high efficiency, a risk of efficiencydeterioration has increased due to increase in contact resistance of thesolar cell.

Solar cells may be connected to each other by a ribbon to constitute asolar cell battery. In this case, low adhesion between electrodes andthe ribbon may cause a large serial resistance and a deterioration inconversion efficiency. Moreover, electrodes fabricated using acomposition for solar cell electrodes including conventional leadedglass frits may exhibit insufficient adhesive strength with respect tothe ribbon.

As described above, a composition according to embodiments may exhibitexcellent adhesive strength with respect to a ribbon connecting solarcells to each other and may minimize serial resistance (Rs), therebyproviding excellent fill factor and conversion efficiency.

Example embodiments have been disclosed herein, and although specificterms are employed, they are used and are to be interpreted in a genericand descriptive sense only and not for purpose of limitation.Accordingly, it will be understood by those of skill in the art thatvarious changes in form and details may be made without departing fromthe spirit and scope thereof as set forth in the following claims.

What is claimed is:
 1. A composition for solar cell electrodes,comprising: a silver powder; an organic vehicle; and a glass fit thatincludes bismuth (Bi), tellurium (Te), and chromium (Cr), Te being thepredominant metal in the glass frit in terms of wt % of the metal oxidewherein the glass frit includes lead oxide in an amount of 0 to 14.5 wt%.
 2. The composition as claimed in claim 1, wherein the glass fritfurther includes at least one element selected from lithium (Li), zinc(Zn), tungsten (W), phosphorus (P), silicon (Si), magnesium (Mg), cesium(Ce), strontium (Sr), molybdenum (Mo), titanium (Ti), tin (Sn), indium(In), vanadium (V), barium (Ba), nickel (Ni), copper (Cu), sodium (Na),potassium (K), antimony (Sb), germanium (Ge), gallium (Ga), calcium(Ca), arsenic (As), cobalt (Co), zirconium (Zr), manganese (Mn),aluminum (Al), and boron (B).
 3. The composition as claimed in claim 1,wherein the glass frit is prepared from a mixture of metal oxidesincluding about 5 wt % to about 30 wt % of bismuth oxide, about 40 wt %to about 80 wt % of tellurium oxide, about 1 wt % to about 15 wt % ofchromium oxide, and about 1 wt % to about 50 wt % of a fourth metaloxide.
 4. The composition as claimed in claim 3, wherein the fourthmetal oxide includes at least one metal oxide selected from lead (Pb),lithium (Li), zinc (Zn), tungsten (W), phosphorus (P), silicon (Si),magnesium (Mg), cesium (Ce), strontium (Sr), molybdenum (Mo), titanium(Ti), tin (Sn), indium (In), vanadium (V), barium (Ba), nickel (Ni),copper (Cu), sodium (Na), potassium (K), antimony (Sb), germanium (Ge),gallium (Ga), calcium (Ca), arsenic (As), cobalt (Co), zirconium (Zr),manganese (Mn), aluminum (Al), and boron (B) oxides.
 5. The compositionas claimed in claim 3, wherein the fourth metal oxide includes about 1wt % to about 10 wt % of lithium oxide, about 1 wt % to about 10 wt % ofzinc oxide, and about 1 wt % to about 10 wt % of tungsten oxide based onthe total weight of the mixture of metal oxides.
 6. The composition asclaimed in claim 1, including: about 60 wt % to about 95 wt % of thesilver powder; about 0.5 wt % to about 20 wt % of the glass frit; andabout 1 wt % to about 30 wt % of the organic vehicle.
 7. The compositionas claimed in claim 1, wherein the glass fit has an average particlediameter (D50) of about 0.1 μm to about 10 μm.
 8. The composition asclaimed in claim 1, further comprising at least one additive selectedfrom a dispersant, a thixotropic agent, a plasticizer, a viscositystabilizer, an anti-foaming agent, a pigment, a UV stabilizer, anantioxidant, and a coupling agent.
 9. The composition as claimed inclaim 1, wherein the organic vehicle includes a binder resin, the binderresin having a weight average molecular weight (Mw) of about 30,000g/mol to about 200,000 g/mol.
 10. The composition as claimed in claim 1,wherein the composition has a viscosity of about 100,000 cps to about500,000 cps.
 11. A solar cell electrode fabricated using the compositionfor solar cell electrodes as claimed in claim 1.